AND SPECIES OE HTDEOIDA. 257 



sarsii, Steenstrup, from which it would seem to difter chiefly in 

 its shorter stem, less numerous proximal tentacles, and longer 

 distal ones, and in the simple common peduncles of its gonophore- 

 clusters. The structure of its gonophores, however, could not be 

 determined with certainty ; and though these appear to develop 

 into true plauoblasts of the Amalthcea type, it was impossible, 

 from a mere spirit specimen, to satisfy one's self entirely on this 

 point. The reference of the Hydroid to the genus Amalthcea ia 

 thus, to a certain extent, provisional. 



One of the most striking features in the present species con- 

 sists in the great length of its proximal tentacles. These nearly 

 equal the entire height of the stem, round which, in the living 

 state of the animal, they must have formed a graceful inverted 

 tassel of flexile filaments, subject to the impulse of every passing 

 current of the surrounding water. 



The thin pellicle which in Amalthcea replaces the strong peri- 

 sarc of other Hydroids, was here irregularly corrugated and sepa- 

 rated by a considerable interval from the ectoderm of the stem ; 

 but this latter state was probably connected with the alcoholized 

 condition of the specimen. 



MONOGAULIBM. 



MoNOCAULirS. 

 MONOCAULUS GRCENLANDICA. Plate IX. figS. 7, 8. 



Trophosome. Hydrocaulus attaining a height of about 1 inch, 

 emitting towards the base numerous capillary filaments. Hy- 

 dranths with the tentacles of the proximal zone moderately long, 

 about twenty in number ; tentacles of the distal zone very short 

 and numerous. 



Gonosome. Gonophores oviform, destitute of tentaculiform ap- 

 pendages, in seven or eight clusters, each cluster consisting of 

 numerous gonophores, which are borne on all sides of a common 

 peduncle, on which they are sessile. 



Locality. Grreenland, collected by Hollboll, Zool. Mus. Cop. 



There can be scarcely any doubt that the gonophores of this 

 Hydroid are simple fixed sporosacs, and that the species is rightly 

 referred to the genus 3Ionocaulus. The pellicle, which takes the 

 place of the perisarc, is somewhat thicker than in Co7-ymorpJia 

 and other so-called naked Hydroids, but is yet very different 

 from the thick firm perisai-c of Tuhularia, Eudendrmm, &c. It 



